The present invention relates to apparatus for molding composite articles from two flowable materials and, more particularly, pertains to an injection molding machine for forming a composite lead and plastic article.
Injection molding machines for forming composite articles of two or more materials are known in the art. Most of the prior art machines are of the multiple mold-multiple station type wherein a first material is injected into a first mold cavity, the first material is moved to a second station where the second material is injected into contact with the first, and the composite article is then moved to another station for removal, usually by positive ejection. Other treatment steps, such as blow molding, may be interposed at stations between the injection and ejection stations. The mold cavities are generally formed and opened after molding by relative reciprocal movement between two mold halves, one of which may be subsequently translated with the first injected material to form a second mold cavity with another mold half, all in a manner well known in the art. Translation of a first molded piece within or on one of its mold halves to a subsequent molding or other station is commonly accomplished by rotation about an axis either perpendicular or parallel to the face of one relatively fixed mold half. Further, it is known to incorporate core pins in the various mold cavities to block the entry of one injected material, which pins are removed at a subsequent station (and replaced with a second set of core pins) to allow another material to be injected into the first core areas to form a composite article. Similar pins are also used to eject finished articles from the molds.
U.S. Pat. Nos. 3,702,750 and 3,832,110 show basically similar two-material article injection molding machines having a pair of mold-carrying platens mounted for relative reciprocal movement and sequential rotary movement to provide two molding stations and an ejection station or position. One of the platens includes two separate sets of fixed core pins which are adapted to be sequentially inserted into first and second mold cavities for formation of a composite article. In U.S. Pat. No. 3,702,750, in addition to the two sets of core pins, a third set of pins is provided for ejecting the composite article. Relative rotation between the platens is provided on an axis perpendicular to the faces of the platens.
U.S. Pat. No. 3,408,691 discloses an injection and blow molding machine in which a rotary mold block is disposed between the mold carrying faces of two relatively reciprocable and opposed platens. The rotary block has an axis of rotation parallel to the mold faces on the platens and is adapted to carry a molded piece from the injection station on one platen to the blow molding station on the other platen. The finished piece is ejected at an intermediate position as the block rotates back to the injection station. The apparatus disclosed in this patent is adapted to form only a one-material article.
In U.S. Pat. No. 3,224,043 a similar machine is disclosed, but which is particularly adapted to form a composite article from two separately injected materials. The intermediate rotary block carries a series of identical mold halves which are adapted to be sequentially carried with a partially formed part from a first injection station on one of the relatively reciprocable platens to the second injection station, diametrically opposite the first on the other platen. The composite parts formed with this apparatus are of a relatively simple configuration and no particular means is disclosed for providing cored regions in the first injected material so that the subsequently injected second material will form an interlocked composite.
U.S. Pat. No. 3,947,176 shows a combined two material injection molding and blow molding apparatus utilizing a rotating center block to transfer the molded articles between stations. Again, however, the composite injection molded article is of simple configuration comprising two layers of plastic injected over a fixed core rod on the rotating block in sequence in stationary split molds.
U.S. Pat. No. 4,118,553 discloses a composite battery grid and method of making such a grid. The composite grid disclosed therein is formed from plastic and a conductive metal, the latter preferably comprising lead. One embodiment of the composite battery grid, shown in this patent, provides for its formation by a method in which the lead portion is molded first with cored areas to subsequently allow the plastic material to be injected over the lead and into the cored areas to provide a positive interlocking of the two materials. In accordance with the disclosed method, one half of the mold used to form a lead-receiving mold cavity is provided with core pins which are extendable into the cavity to prevent the receipt of lead into the cored areas of the lead cavity. The core pins are retractable and the mold half with the retracted pins is subsequently movable along with the molded lead part into engagement with a plastic-receiving mold half to form a composite material mold cavity. Plastic material injected into this cavity fills the plastic-receiving half as well as the cored areas of the lead half vacated by the retracted core pins, resulting in a composite interlocked lead and plastic construction.
Multiple mold-multiple station injection molding apparatus of the prior art, typified by the above identified machine patents, have been found unsuitable to provide composite articles of the construction disclosed in U.S. Pat. No. 4,118,553.
Those composite molding machines in which one of the platens rotates with respect to the other about an axis perpendicular to the mold faces (e.g. U.S. Pat. Nos. 3,702,750 and 3,832,110) require the injection of both materials from the fixed platen end. Where the two materials are very dissimilar and require substantially different injection equipment, injecting both materials from the same side may be extremely difficult or impossible. This is particularly the case where the materials are plastic and metal. In addition, these prior art machines require a separate set of core pins for each injection station and for the part ejection, if pins are used for this latter purpose.
In the other type of prior art composite article molding apparatus, in which a rotary block carries mold halves with the sequentially moldable composite articles between other mold halves on opposed and relatively reciprocable platens (e.g. U.S. Pat. Nos. 3,224,043 and 3,947,176), there is disclosed no means for moving core rods or pins within and relative to the rotary block. In order to form a complex composite article of the type shown in U.S. Pat. No. 4,118,553, it is desirable for a number of reasons that movable core pins be disposed within the mold half receiving the first injected material, which mold half carries the partially molded article to a subsequent injection station to form half of the mold cavity for receipt of the second injected material. First, the core pin ends may be shaped to form undercut recesses in the back face of the first molded material to allow receipt and positive locking of the second molded material. Second, the pins can be retracted and stripped from the first material without dislodging it from the mold half which must carry it to the second material injection station. Third, the retracted pin ends can provide a barrier in the mold cavity for receipt of the second material to prevent its flow beyond the back face of the first molded material. And fourth, the core pins may be utilized to eject the composite article.